Method of using a composite joint infill system

ABSTRACT

A pair of concrete coated pipe joints welded together end to end with a gap between the concrete coatings, the gap being filled with a fast setting elastomeric polymeric infill material, either solid or foamed, and a particulate filler material, and a method for molding the infill material with the mold being filled with filler material before the polymer components are injected, and with a membrane lining the mold to prevent the polymer from adhering to the mold.

This invention relates to a means and a method for infilling the spaceat a welded joint in a concrete coated pipeline between the ends of theconcrete coatings on sequential joints of pipe.

BACKGROUND OF THE INVENTION

Offshore pipelines are commonly laid from a continuously moving vesselknown as a lay barge. The separate lengths of pipe in the pipeline maybe welded together on shore and then coiled on a reel and placed on alay barge for the pipe laying operation. Alternatively, lengths of thepipe may be placed on the lay barge and welded together on the bargejust prior to laying the pipeline. In either case, to lay the pipelineone end of the line is passed over rollers and then down an elongatecradle or "stinger" which extends rearwardly and downwardly from thestern of the lay barge to the bed of the body of water. As the bargemoves forward, the forward motion of the barge causes the pipeline to bepulled along the rollers and down the stinger and thereby continuouslylaid on the bed of the body of water.

Pipelines larger than about 12 inches in diameter are commonly coatedwith a thick layer of concrete to weight the pipeline down in the water.Such concrete coatings are applied to individual lengths of the pipewith the coating extending the full length of the pipe except forseveral inches near each end. Prior to applying the concrete coating,the pipe lengths are usually coated with a material, such as epoxy, toprotect the pipe from corrosion. This coating material is alsoterminated several inches from each end. Successive lengths of pipe arejoined together by welding, leaving a gap in the coating material and inthe concrete covering at each joint. It is the usual practice to apply acoating to the pipe in this gap to protect the pipe against corrosion,for example with a hot fusion bonded epoxy and/or a shrink sleeve, andto fill the gap between the ends of the concrete coatings so as toprovide a smooth, uninterrupted covering for the pipeline. The pipelinecan then move smoothly over the rollers and down the stinger to the seabed.

The gaps are filled with various materials by various techniques. Oneprocedure is to place a metal sleeve or mold over the gap and fill thesleeve with molten mastic which solidifies as it cools. However, in mostcases the pipeline must be in a condition for handling immediately afterthe gaps are filled, so that the laying of the pipeline can proceedwithout delays. The mastic filling does not set to a sufficiently strongmaterial within the required time to allow further processing of thepipe without additional reinforcement to protect the mastic. Therefore,in conventional filling operations where mastic is used, the sleeve isleft in place, so that it remains on the pipe on the ocean floor. Thisis objectionable, since the sleeve can snag fishnets, and cause otherdamage to marine operations. Moreover, the filling of the gaps withmastic in this way is highly labor intensive, and therefore expensive.

A more effective method is to fill the gap with a fast cure materialinside a removable, preferably reusable, mold which is removed beforethe pipe is advanced into the water. Various polymer concretes, such asthose disclosed in U.S. Pat. No. 4,608,208, or polyurethanes have beenused in this way. The removable mold surface is coated with a releaseagent to prevent the fast cure material from sticking to the moldsurface. Such a mold release adds expense and processing time, and isinefficient if improperly applied. Furthermore, some of the releasematerial remains on the surface of the fast cure material and enters thewater with the pipe as a potential environmental contaminant.

SUMMARY OF THE INVENTION

According to the present invention the gap between the concrete coatingson successive pipe lengths is filled by molding in place a fast settingelastomeric polyurethane or polyurea, either foamed or solid, whichincludes a uniformly dispersed filler material. Such a joint infill hasexcellent adhesive properties, bonding directly to most dry materialsand substrates, and can be applied directly over hot fusion bonded epoxyor a shrink sleeve with little or no effect on corrosion protection.Once solidified, the material becomes an environmentally and chemicallyneutral, stable high strength product. Within five minutes of casting,the pipe with the infill of this invention can be pulled over guiderollers and down a stinger or across a beach or ocean bottom.

In molding the joint infill of this invention, an expendable, orreusable, sheet or clam type mold can be used, depending on theparticular material selected. Preferably, a reusable metal clam typemold is used, with a low cost, bio-degradable membrane, such as a sheetof cardboard, used to prevent the polymeric material from contacting andadhering to the mold, to allow easy separation of the mold from themolded product.

The mold is first filled with the filler material, and the unreactedcomponents of the polyurea or polyurethane are fed into the mold througha tube inserted into the top of the mold and extending into the bottomof the mold cavity. As the unreacted materials flow into the moldcavity, the tube is slowly withdrawn so that it will not be caught inthe solidifying polymer, with flow of the unreacted polymer componentscontinuing until the filler material is fully saturated and the mold isfilled. The low viscosity of the mixture of unreacted polymer componentsallows it to fully eliminate all voids by filling the intersticesbetween the filler material particles.

When a solid joint infill material is to be molded, the mold may consistof merely a sheet of polyethylene or polypropylene wrapped around thegap and overlapping the ends of the concrete, with the ends of the sheetnot quite reaching each other at the top of the gap. This sheet is thensecured in place by clamps wrapped around it over the enclosed ends ofthe concrete. A polymer filler tube is inserted into the opening at thetop of the mold, and run to the bottom of the mold. The filler materialis poured in until the mold is filled, and the mixed components of thepolymer are then injected through the tube to fill the mold, includingthe interstices between the particles of filler material, from thebottom up, with the filler tube being withdrawn as the mold is filled.When the mold is filled, the flow of polymer components is stopped, andthe polymer is allowed to set up. In from two to five minutes, the moldsheet may be removed, and the pipe is ready to handle.

When a foamed polymer is used, it is preferred to use a steel mold sothat pressure can be held on the polymer during the foaming and settingof the material. This mold is preferably lined with a membrane toprotect the mold from the polymer, so that the mold can be easilyremoved after the molding is finished. A preferred membrane iscardboard, which will adhere to the polymer, but will prevent thepolymer from adhering to the mold. The mold is filled in the same way,but when filling is completed, the opening at the top is clamped shut tohold the material under pressure until it sets up.

It is therefore an object of this invention to produce a joint infillsystem superior to those previously available in resistance to injury,and which is relatively inexpensive.

A further object of this invention is to produce such a joint infillsystem which can be molded in place and will set up in a short time sothat the pipeline can be handled almost immediately.

Still another object is to provide a method for forming an infill forpipe joints which allows the use of a reusable mold which is easilyremoved from the molded infill and which does not require a releaseagent which may contaminate the environment.

Another object of the invention is to provide a superior mold protectingmembrane which can be left on the molded joint infill, and will allowthe mold to be reused.

The accomplishment of these and other objects of the invention willbecome apparent from the following description of the preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawing is a longitudinal sectional view of a portion of apipeline showing one embodiment of the joint infill of this invention;

FIG. 2 is a perspective view of a portion of the pipeline showing a moldin place for forming the joint infill according to one embodiment ofthis invention;

FIG. 3 shows a mold according to another embodiment of the invention;and

FIG. 4 is a vertical sectional view of a mold mounted to mold the jointinfill according to one embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of the drawing shows a segment of a pipeline 10 includingsequential pipe joints 12, 14 welded together at 16. Each pipe length iscovered with a concrete coating 18 which terminates short of theadjacent ends of the pipe lengths, leaving a gap 20. A shrink sleeve 22covers the weld and extends axially along each pipe length for severalinches. The shrink sleeve is usually made of an extruded heat shrinkableplastic sheet or tape which is wrapped around the pipe to completelycover the area which is not protected by the corrosion resistant coatingwhich has previously been applied to the pipe. Heat is then applied toshrink the sleeve to cause it to fit tightly around this area. The gapis then filled by the joint infill 24 of this invention.

As shown in FIG. 2, the filling of the gap is accomplished by installinga mold around the gap. If a solid polymer is to be used, the mold mayconsist of a sheet 24 of polyethylene, polypropylene or other materialto which the polymer to be cast will not adhere, wrapped around the pipewith an opening 26 at the top through which the filler material and thepolymer components can be placed into the mold space. The mold may besupported by a mold support cart 30 consisting of a rectilinear frame 32mounted on wheels which support the cart on the concrete coating of thepipe. Straps 38 are attached to the longitudinal members 36 of the frameand wrap around the mold sheet 24 at each end to hold the mold sheettightly against the concrete coating. Means not shown may be used totighten the straps, and the straps preferably are readily releasable atone end. A filler tube 28 is inserted through the frame and the opening26 at the top of the mold sheet. Once the mold is in place, the gap 20between the ends of the concrete coating is filled with a granular orparticulate filler material, and unreacted polymer is fed into the moldspace through the tube 28. As the polymer fills the mold, the tube isgradually withdrawn so that it will not be held in the mold by thehardening polymer. When the polymer reaches the top of the mold, it issmoothed out by hand to form a continuous cylindrical surface.

FIG. 2 also shows a schematic drawing of a mixing valve for providing amixture of polymer components to the mold. The valve 50 includes aninlet 52 for one of the components, an inlet 54 for the other component,an air inlet 56 and an outlet 58. The valve is suspended with the outlet58 above the mold. The fill tube 28 extends from the outlet 58 throughthe opening in the top of the mold down to the bottom of the mold spacewhen the molding operation begins.

The preferred polymers of this invention are fast setting, i.e. theywill set up in five minutes or less sufficient for the mold to beremoved. The mold is removed by loosening the straps 38 and rolling thecart longitudinally of the pipeline to the next joint to be filled.

If a foamed product is to be produced, a steel mold is preferred. Asshown in FIG. 3, such a mold may consist of a sheet steel cylinder 40with an arcuate closure segment 42 hinged to it so that it may be openedto fill the mold. The partial cylinder 40 is placed around the pipe bysliding it on one end, or it may be made of a material resilient enoughthat it may be opened up to allow it to be placed around the pipe.Alternatively, the partial cylinder may be made in two halves, hingedtogether by a longitudinally extending hinge. In either case, it ispositioned to enclose the gap to be filled, with the ends of thecylinder covering the ends of the concrete coating 18 on each joint ofpipe, thereby enclosing an annular mold space 44 within the mold andsurrounding the pipe between the ends of the concrete coating. Amembrane 46, as shown in FIG. 4, lines the steel mold and protects itfrom contact by the polymer. The membrane is clamped between the ends ofthe mold and the ends of the concrete coating by the straps 38 at eachend of the mold. Preferably a gasket or seal 48 is interposed betweenthe mold ends and the concrete coating to prevent the liquid polymercomponents from leaking out when the mold is filled. The gasket maycomprise an adhesive tape with adhesive on one side or both sides. Theentire assembly is then supported on a cart 30 with the straps 38 as inthe previous embodiment.

As in the previous embodiment, a filling tube 28 is placed into the moldspace, extending substantially to the bottom, and the mold space is thenfilled with the filler material. The foaming polymer material is thenplaced into the mold through the tube 28, with the tube being withdrawnas the mold is filled. When the mold is filled with a predeterminedamount of the polymer material, the segment 42 is placed over the gap inthe partial cylinder 40, and clamped down to close the mold. The polymerfoams and sets up enclosed in the mold. After five minutes or less, thestraps 38 may be loosened, the mold segment 42 may be opened, and themold may be removed from the molded joint infill. The membrane mayadhere to the joint infill, but the mold parts are protected from suchadherence.

The joint infill material of this invention is preferably made of a fastsetting elastomeric polymer which will set up in a few minutes so thatthe pipe can be handled without fear of damage to the joint infill.Preferred polymers include the rapid setting solid polyurethanes, as forexample those prepared by the reaction of the polyhydroxyl containingcompounds and the organic polyisocyanates described in U.S. Pat. Nos.3,983,064, 4,154,716 and 4,246,363, the disclosures of which areincorporated herein by reference. Other suitable polymers include therapid setting polyureas, for example those prepared by the reaction ofamine terminated polyethers and the organic polyisocyanates described inU.S. Pat. No. 4,474,900.

The polymers of this invention also preferably include a filler materialor aggregate, for the purpose of adjusting the weight of the infill, andalso to reduce the amount of expensive polymer required. Suitableaggregates include gravel or iron ore, of from 1/16 inch to one inchmesh, preferably 1/8 inch to 1/2 inch, chopped-up tires, wood chips, orany other available particulate solid material which will not pack solidof its own weight.

The compositions of this invention preferably also include a liquidmodifier, such as those described in the aforesaid patents. In addition,the compositions preferably include a liquid organic carbonate, and asufficient amount of one or more catalysts to insure that thecomposition will set up in not more than about five minutes.

The reactants to produce these polymers have a low viscosity, notgreater than about 100 centipoises, before polymerization, so that whenthey are fed into a mold to form the joint infill, they willsubstantially completely fill the interstices between the granularfiller materials.

In preparing the preferred polyurethanes, preferably an amine initiatedpolyol is used and more preferably a polyol is selected which has ahydroxyl number in the range of about 600 to about 900 and a minimumfunctionality of 4. One such material which can be obtained from DowChemical Company at Freeport, Tex. is sold under the trademark Voranol800 and is the product of reacting ethylene diamine with 3 parts ofpropylene oxide and one part of ethylene oxide.

For the rapid setting polyureas, it is preferable to use an amineterminated polyether which has an equivalent weight in the range of 50to 100 and a minimum functionality of 3.0. One such material which canbe obtained from Texaco Chemical Co. is sold under the trademarkJEFFAMINE T-403 and is fully described in U.S. Pat. No. 4,474,900.

The polymeric isocyanate used is preferably one which has a high vaporpressure for safety purposes. Dow Chemical Company sells a suitablematerial under the trademark PAPI 27 which is a crude polymericisocyanate containing some methylene bis phenyl isocyanate and 50-60%polyethylene polyphenyl isocyanate.

The liquid modifier used is preferably a heavy aromatic petroleumdistillate consisting primarily of C9 to C11 aromatic hydrocarbons,having a flash point of at least about 200° F. to 230° F. Such a productis available from Arco Chemical Company division of Atlantic RichfieldCompany under the designation H.A.S. (heavy aromatic solvent).

The liquid organic carbonate used may be one of those described in U.S.Pat. No. 4,154,716. Propylene carbonate has been found to give goodresults. The organic carbonates are known as plasticizers, and in thecomposition of this invention they reduce the propensity of thecomposition to shrink as it cures, and therefore reduce the tendency ofthe product to crack under stresses produced during curing. Otherplasticizers which have been tried do not produce this advantageousresult.

In a particularly preferred embodiment of the invention, a foamedpolyurethane or polyurea is used. Foaming extends the range of densitieswhich can be obtained, and allows a greater reduction in the amount ofpolymer required, without reducing the strength or impact resistance ofthe infill to an undesirable extent. Thus, with sufficient foaming, thedensity of the material may be reduced to one-third its unfoamed densityof about 66 lbs. per cubic foot, requiring only one-third as muchpolymer. If weight is important, the density can be increased by addinga heavy aggregate, such as iron ore, to increase the density to as muchas 120 lbs. per cubic foot. When a foamed material is used, the volumeof the space to be filled is calculated, taking into account the spaceoccupied by the filler material, and an amount of polymer components isintroduced into the mold which will produce the desired density offoamed material when it foams to fill the mold.

The foamed polyurethanes of this invention are prepared similarly as theunfoamed polyurethanes, except that a foaming material is added. Wateris a suitable foaming material, as well as various other low-boilingpoint materials which will boil at the reaction temperature.

The reactants for preparing the compositions of the invention arepreferably prepared as two components. Component A consists of thepolymeric isocyanate combined with the liquid modifier and a liquidorganic carbonate. Component B consists of the polyhydroxyl compound orpolyether combined with the liquid modifier and a small percentage ofthe liquid organic carbonate, together with an amount of catalystsufficient to insure that the composition will set up in no more thanabout five minutes.

The catalyst used for polyurethanes may be any of the well knowncatalysts for polyurethane. A number of such catalysts are described inU.S. Pat. No. 4,246,363. The preferred catalysts for the polyurethanecomposition of this invention are approximately 0.1% to about 0.5% of a1-2 mixture of triethylene diamine and dipropylene glycol together withabout 0.01% to about 0.04% of an alkyl tin mercaptide such as that soldby Witco Chemical Company as their UL-22 catalyst.

When the foamed product is to be produced, a small amount of water, fromabout 0.1% to about 4.0%, and preferably in the range of about 1.8% toabout 2.8%, is added to Component B. The amount of water used will bevaried depending on the desired density of the final product.

The ingredients of Components A and B are mixed separately and held atessentially ambient temperature until ready for use, although theyshould be protected from extreme cold or extreme heat, becausetemperature affects the speed of reaction. In use, the two componentsare mixed as they are pumped into the mold where the product of theinvention is to be made, as previously described.

When the mold has been put in place, it is filled with the particulatefiller material and the two components A and B are then pumped throughthe conduits 52 and 54, and mixed within the valve 50, and the mixtureflows into the bottom of the mold through the tube 28. This mixture hasa very low viscosity, usually not greater than about 100 centipoises, sothat it flows readily into the mold space and between the intersticesbetween the particles of the filler material. When the mold is filled tothe desired extent, the valve may then be cleaned out by blowing airthrough the conduit 56 in order to prevent the material from solidifyingwithin the valve and the conduits. A check valve 59 prevents the liquidcomponents from entering the air inlet conduit 56.

After the mold is filled, the composition will set in a very short time,preferably not over about 5 minutes, and the mold sheets can then beremoved. If a steel mold with a membrane mold protector has been used,the mold comes off easily. A polyethylene or polypropylene membrane willalso come off easily, since these materials do not adhere to thepolyurethane or polyurea. If a cardboard membrane has been used, it willadhere to the infill material.

As previously noted, with a steel mold, means must be provided toprevent the polymer from adhering to the mold. In the past, a releaseagent, such as wax or oil, has been used for this purpose. However, suchrelease agents are undesirable for underwater installations, because thewax or oil causes pollution of the water. Preferably, a membrane is usedto line the mold and prevent the polymer from contacting the mold. Suchmembranes may be made of a sheet material such as polyethylene orpolypropylene, and may be from about 0.003 inch to 0.250 inch or morethick. Preferably, however, the membrane consists of fibers, shreds or amesh of natural or synthetic materials, woven or adhered together toform a pad, sheet or cloth which can be stacked or rolled for storage.Binders and/or adhesives may be used to enhance the structure of themembrane.

The material used for the membrane may be prepared from naturalmaterials, such as mineral fiber, cotton, wool or silk, or from naturalmaterials which have been processed, such as cellulosic based productssuch as those used to form paper or cardboard, or mixtures of suchmaterials. The cellulosic materials may include wood, or woodby-products, hydroxyethylcellulose, carboxymethylcellulose orhydroxyalkylcelluloses, or mixtures of such materials. Suitable membranefibers, shreds, or meshes may also be prepared from synthetic materials,such as polyesters, polyurethanes, nylon, rayon, acetates, polyamides,polyacrylonitriles, polyvinyl alcohol or polyolefins. Inorganicmaterials, such as glass, may also be used, as in glass fibers or a meshof glass fibers. Combinations of natural, synthetic and inorganic fibersmaterials may be used with or without special surface treatments. Also,reclaimed or recycled materials can be used as a material base for themembrane of this invention.

A preferred material for the membrane of this invention is cardboard,including corrugated paperboard. Such materials may be used inthicknesses of from about 0.005 inch to one inch, but preferably are inthe range of 0.015 inch to 0.5 inch, and more preferably are from about1/8 inch to about 1/4 inch. The cardboard provides a barrier between thefast cure material and the mold surface, preventing the fast curematerial from contacting the mold surface and adhering to it, so themold surface is reusable. Instead, the cardboard adheres to the fastcure material. A properly formulated fast cure material saturates aportion of the cardboard, but does not penetrate it, providing acomposite skin to the resultant cutback fill which improves the abilityof the joint infill to withstand various physical abuses which resultfrom insertion of the pipe into the water or ground. These physicalabuses vary from rollers on a stinger assembly to land and underwaterprojections which the pipe may encounter as it is dragged off-shoreand/or settles on the land surface or subsea surface. Moreover, thecardboard does not provide a marine hazard to fish nets, for example,and a biodegradable cardboard can be used for environmental purposes.

The use of a cardboard membrane also makes it practical to use jointinfill materials which exhibit slow surface cure; that is, have asurface which remains tacky or sticky for a long period. The membrane ofthe invention negates the slow surface cure problem as the reactionmaterial is no longer in contact with the mold surface or any othersurface (i.e., wheels, rollers, slide rails) to which the slow curesurface would stick. The membrane adheres to the surface of the slowcure material which isolates and prevents the slow cure material fromadhering to other surfaces.

Some membrane materials may also provide a gasket between the interiorsurface of the mold and the exterior surface of the concrete weightcoating, thereby eliminating the necessity for a seal for reducing orpreventing leakage of the liquid fast cure, medium cure or slow curecomponents prior to solidification.

EXAMPLE 1

In preparing a solid polyurethane according to this invention, componentA is prepared by mixing 60 pounds of a polyisocyanate sold under thetrademark PAPI 27 by Dow Chemical Company, 30 pounds of Shell ChemicalCompany's SC-150 Solvent, and 10 pounds of propylene carbonate.Component B is prepared by mixing 31 pounds of Dow Chemical Company'sVoranol 800, 64 pounds of the SC-150 Solvent, 5 pounds of propylenecarbonate, 0.08 pounds of a catalyst consisting of 1/3triethylenediamine and 2/3 dipropylene glycol, and 0.002 pounds of analkyl tin mercaptide sold by Witco Chemical Company under thedesignation UL-22 catalyst. The two components are kept separate fromeach other until they are to be used, and are kept at atmospherictemperature.

When the product is to be molded, separate pumps are used to pump thecomponents into a mixing valve, where they are mixed together and thenfed into a mold made of polyethylene sheet, until the mold is filled.After a wait of five minutes, the mold is removed, leaving a solid jointinfill which is highly resistant to injury from sharp blows. The jointinfill is also securely adhered to the pipe and to the adjacent ends ofthe concrete coating.

EXAMPLE 2

In preparing a solid polyurea according to this invention Component A ispreparing by mixing 64 pounds of the PAPI 27 polyisocyanate, 26 poundsof SCI50 solvent, and 10 pounds of propylene carbonate. Component B isprepared by mixing 31 pounds of JEFFAMINE T-403, 64 pounds of the SC150solvent, 5 pounds of propylene carbonate, 0.08 pound of catalystconsisting of 1/3 triethylenediamine and 2/3 dipropylene glycol, and0.002 pound of Witco's UL-22 catalyst. The components are handled thesame way as in Example 1, producing a fast-setting polyurea. Fiveminutes after pouring into the mold, the mold is removed, resulting in asolid joint infill which is highly resistant to injury by sharp blows.

EXAMPLE 3

In preparation of a foamed joint infill, Component A was prepared byadmixing 92 pounds of Dow's PAPI 27 polymeric isocyanate with 8 poundsof Arco's H.A.S. solvent. Component B is prepared by mixing 27 pounds ofDow's Voranol 800, 61.3 pounds of the H.A.S. solvent, 6.4 pounds ofethoxylated nonyl phenol, 0.3 pound of a 1:2 mixture oftriethylenediamine and dipropylene glycol, 2.5 pounds of Union Carbide'sL-5420 silicone surfactant, 0.023 pound of Witco's UL-22 alkyl tinmercaptide catalyst and 2.45 pounds of water.

Two joints of 24" diameter pipe having a 3 inch thick concrete coatingwere welded together, leaving a 24 inch distance of bare pipe betweenthe ends of the concrete coatings. The bare pipe was coated with hotmelt epoxy, and a polyethylene shrink sleeve was installed around theweld. A removable steel mold was fitted with a sheet of cardboardmembrane (1/8" thick) on the inside surface of the mold and the moldwith the cardboard membrane wrapped around the gap between the ends ofthe concrete coating. The mold and cardboard membrane was 30 inches longand overlapped the concrete on each end by 3 inches. The mold wastightened around the overlapped concrete with straps and locked withquick release buckles. The top of the mold was fitted with a hingedclosure to allow for entrance of a mold fill material.

The mold space is filled with a 1/4 inch pea gravel aggregate, thevolume of the remaining mold space is calculated, taking into accountthe volume occupied by the pea gravel, and equal volumes of Compounds Aand B are measured out, sufficient to total one-third the volume of themold space. The separate components are fed in equal volumes through ablending valve and through a tube inserted into the bottom of the mold.The opening in the top of the mold is covered by a cardboard membrane,and the closure is closed and clamped shut. The polyol resin blend andisocyanate reacted and formed an open cell, polyurethane polymer foamwhich filled the cutback void. The resultant polyurethane foam adheredto the pipe, concrete edges and the cardboard membrane but not to themold surface. The mold was removed 21/2 minutes after injection of thepolyurethane fast cure material. Upon mold removal, the mold fell freeof the fast cure polyurethane foam and cardboard membrane with thecardboard adhered to the surface of the polyurethane foam, providingimproved exterior protection to the resultant joint. The mold was foundto be clean and free of any polyurethane foam fast cure material whichrendered the mold reusable.

This invention is not limited to the specific embodiments shown anddescribed, but instead includes all variations included within the scopeof the following claims.

We claim:
 1. A method for forming a joint infill at the juncture ofsequential lengths of concrete coated pipe welded together end to endwith a gap between the concrete coatings which comprisesenclosing thegap with a mold having a top opening, filling the mold with aparticulate filler material, then injecting into the mold a mixture ofunreacted liquid components of a rapid setting elastomeric polymer,allowing the components of the polymer to react until the polymer setsup, and removing the mold.
 2. A method as defined by claim 1 wherein theelastomeric polymer is a foamed material.
 3. A method as defined byclaim 1 and including lining the mold with a membrane before fillingwith the particulate material.
 4. A method as defined by claim 3 inwhich the membrane is made of cardboard.
 5. A method as defined by claim1 in which the mold is made of a material to which the polymer will notadhere.
 6. A method as defined by claim 2 in which the mold is made ofsteel and includes a closure which is held closed while the polymericcomponents react.
 7. A method as defined by claim 1 including insertinga filler tube substantially to the bottom of the space enclosed by themold before introducing the particulate material, and withdrawing thefiller tube during the injection of the polymer components into the moldspace, where by the mold is filled with the polymer components from thebottom up and the filler tube is removed before the polymer sets up.